Another case there alt="" isn't liked by ahrefs.

Author: rouilj

doc/html_extra/original_overview.html

@@ -115,7 +115,8 @@ <h2><a name="overview">Overview</a></h2>
 
 <p align=center>
 <a href="images/roundup-1.png">
-<img src="images/roundup.png" width=358 height=205 border=0 alt=""></a>
+<img src="images/roundup.png" width=358 height=205 border=0
+     alt="Web page with a green banner at the top titled Index of Bugs. Checkboxes to filter issue selection and a table of displayed issues, grouped by severity."></a>
 
 <p><hr>
 <h2><a name="background">Background</a></h2>